Study of equatorial ridge on Iapetus suggests exogenic origin

Apr 21, 2014 by Bob Yirka report
Raw image from Cassini space probe of the equatorial ridge on Saturn's moon Iapetus. Image: NASA

(Phys.org) —A combined team of researchers from Brown University in Rhode Island and the Lunar and Planetary Institute in Texas is suggesting in a paper they've uploaded to the preprint server arXiv, that an equatorial mountainous ridge on one of Saturn's moons has an exogenic origin. They are basing their theory on 3D models of the moon they've created and an analysis of the types of peaks present.

Iapetus, the 3rd largest of Saturn's approximately 60 moons, is distinct for two reasons. One is its odd two-tone coloring; the other is the back-bone looking mountain range straddling part of its equator. Scientists have been puzzled by the origin of the mountain range as the moon doesn't have other geologic qualities that could have given rise to it, such as shifting plates or . Thus, some have suggested that the mountains came from above, rather than below, or in other words, they have an exogenic origin, meaning they came from somewhere else.

To gain a better understanding of the , the research team built a 3D model of it on a computer in their lab, faithfully replicating the 12 mile high by 12 mile wide by 800 miles long range in miniature, using data from the Cassini space probe. Once created, the team set to work measuring the shape of the peaks, which they believed should offer clues as to their origin. They found that the majority of the peaks sat in what is known as their angle of repose, which is the maximum angle at which material can rest on a peak without falling down to its base. Normal geologic activity tends to create peaks that are shallower and have less uniformity. This suggests, the researchers claim, that the mountains did not form due to geologic activity but more likely are part of a ring of material that once circled the moon and was pulled down to the surface.

A ring around the moon would most likely have come about due to a collision, either between another body and the , or two other bodies nearby. The resulting material would have formed a ring around the equator which over time, would have been pulled to the surface by gravity. Such a theory, the team notes, would also explain Iapetus's asymmetrical orbit and also why it orbits with the same face pointing at Saturn all of the time.

Explore further: NASA Cassini images may reveal birth of a Saturn moon

More information: Topographic Constraints on the Origin of the Equatorial Ridge on Iapetus, arXiv:1404.2337 [astro-ph.EP] arxiv.org/abs/1404.2337

Abstract
Saturn's moon Iapetus has an equatorial ridge system, which may be as high as 20 km, that may have formed by endogenic forces, such as tectonic and convective forces, or exogenic processes such as debris infall. We use high-resolution topographic data to conduct a topographic analysis of the ridge, which suggests a predominantly triangular morphology, with some ridge face slopes reaching 40 degrees, allowing for an exogenic formation mechanism.

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User comments : 12

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katesisco
1.3 / 5 (14) Apr 21, 2014
I think maybe that the mountain range is the result of an upward pull perhaps from a strong electromagnetic source. From where? Perhaps the unknown LT starbit aka black hole or an event involving our sun, Sol, exerting a heretofore unidentified quality.
shavera
4.9 / 5 (17) Apr 21, 2014
So... you think, for no good reason whatsoever, that the material was pulled up by... some other thing that you must invent entirely to explain why the material was pulled up.... That's not how science works, sorry.
roblabs
3.9 / 5 (7) Apr 21, 2014
So... you think, for no good reason whatsoever, that the material was pulled up by... some other thing that you must invent entirely to explain why the material was pulled up.... That's not how science works, sorry.


best retort ever.
Returners
1.3 / 5 (13) Apr 21, 2014
So... you think, for no good reason whatsoever, that the material was pulled up by... some other thing that you must invent entirely to explain why the material was pulled up.... That's not how science works, sorry.


Could have fooled me, refer to Dark Matter and Dark Energy.

I don't know what process made Lapetus' mountains, nor does it matter. There are far more pressing and interesting things in the solar system and on Earth for scientists to study, rather than some unimportant mountain range on an unimportant object..
no fate
1 / 5 (5) Apr 21, 2014
So... you think, for no good reason whatsoever, that the material was pulled up by... some other thing that you must invent entirely to explain why the material was pulled up.... That's not how science works, sorry.


Could have fooled me, refer to Dark Matter and Dark Energy.

I don't know what process made Lapetus' mountains, nor does it matter. There are far more pressing and interesting things in the solar system and on Earth for scientists to study, rather than some unimportant mountain range on an unimportant object..


I actually have to go with this one as the best retort ever. With Shavera's a close second.
Caliban
5 / 5 (9) Apr 21, 2014


I don't know what process made Lapetus' mountains, nor does it matter. There are far more pressing and interesting things in the solar system and on Earth for scientists to study, rather than some unimportant mountain range on an unimportant object..


Uh, yeah...but I bet if they had theorized instead --and more specifically-- that the ring of material had been formed from a large cometary/asteroid collision near Iapetus, that this would have gotten your attention and added a little more significance or importance to this science in terms of its relevance for life on Earth, yes?

These collisions not only happen near Earth, they are known to happen with Earth.

How important do you think would be the effect of the deposition from nearth-Earth space onto the Earth's surface of a twelve mile high, twelve mile wide, 800 mile long mountain chain?
antialias_physorg
5 / 5 (3) Apr 22, 2014
They found that the majority of the peaks sat in what is known as their angle of repose, which is the maximum angle at which material can rest on a peak without falling down to its base.

So the ring is more of a dune than a mountain?
Should include an impactor if we get someting flying that way again.

A 12 mile high dune on a moon that tiny in size. The view from up there must be freaky (apart from having Saturn hanging in the sky, of course)
kelman66
not rated yet Apr 22, 2014
I thought I heard this hypothesized a long time ago.
I guess that angle of repose info was missing.
Caliban
5 / 5 (2) Apr 22, 2014
They found that the majority of the peaks sat in what is known as their angle of repose, which is the maximum angle at which material can rest on a peak without falling down to its base.

So the ring is more of a dune than a mountain?
Should include an impactor if we get someting flying that way again.

A 12 mile high dune on a moon that tiny in size. The view from up there must be freaky (apart from having Saturn hanging in the sky, of course)


AA,

Sort of. But think of it more like a pile-up of debris from a collision occuring somewhere in Iapetus' orbit --or orbital path-- and then fell onto the surface, like sand in an hourglass.
Whydening Gyre
5 / 5 (1) Apr 22, 2014
[Sort of. But think of it more like a pile-up of debris from a collision occuring somewhere in Iapetus' orbit --or orbital path-- and then fell onto the surface, like sand in an hourglass.

sort of seems like that would leave more of a mounded pile than precipitously "stacked" debris.
I'm just sayin'...
Captain Stumpy
5 / 5 (1) Apr 23, 2014
sort of seems like that would leave more of a mounded pile
@Whydening Gyre
IDK
IMHO... if we take the quote form the article
but more likely are part of a ring of material that once circled the moon and was pulled down to the surface
and assume some rotation to the ring while adding in the quote from the study
In addition to the three morphological types already classified - triangular, trapezoidal, and crowned peaks - (Porco et al., 2005; Castillo-Rogez et al., 2007; Giese et al., 2008), we find three additional ridge shapes: a twinned morphology, a dissimilar morphology, and a saddle morphology
and since we think Iapetus is tidally locked (see Wiki) then I would surmise that as the moon circled Saturn and had other moons/material disturb the ring, material gradually drifted down to the planet surface which would pile and make the requisite formations per the study over time.

just speculatin', mind you
cantdrive85
1 / 5 (4) Apr 24, 2014
I'm sure it's just a coincidence that Iapetus looks nearly identical to a ridged moqui marble, just on a larger scale.

https://www.googl...bih=1075

It is likely the same process that creates Martian "blueberries", moqui marbles, and large spherical concretions such as these;

https://www.googl...bih=1075

...created Iapetus.

Physicists using electric discharge in plasma were able to mimic such a morphology in the lab;
http://meetings.a...nt/29058